As a typical speaker device, there is known a dynamic speaker device as disclosed in JP-A No. 1996-149596 (FIG. 1) for example. As shown in FIG. 1, the dynamic speaker device described in this patent document includes a frame 3J; a cone-shaped diaphragm 21J; an edge 4J through which the diaphragm 21J is supported by the frame 3J; a voice coil bobbin 610J joined to the inner periphery of the diaphragm 21J; a damper 7J through which the voice coil bobbin 610 is supported by the frame 3J;
a voice coil 611J wound around the voice coil bobbin 610J; a yoke 51J; a magnet 52J; a plate 53J; and a magnetic circuit having a magnetic gap in which the voice coil 611J is placed.
In this speaker device, when an audio signal is input to the voice coil 611J, the voice coil bobbin 610J vibrates by a Lorentz force developed in the voice coil 611J and the vibration is transmitted to the diaphragm 21J to vibrate the same.
The typical dynamic speaker device described above is configured such that, as shown in FIG. 1, the voice coil 611J is disposed opposite to the sound emission side of the diaphragm 21J, and the vibration direction of voice coil 611J and voice coil bobbin 610J is parallel to the vibration direction of the diaphragm 21J. Since the speaker device of this configuration requires, for example, a region for vibration of the diaphragm 21J, a region for vibration of the voice coil bobbin 610J, and a region for disposing the magnetic circuit, the length (total height of the speaker device) in the vibration direction (sound emission direction) of the diaphragm 21J is relatively large.
Specifically, as shown in FIG. 1 for example, the dimension in the vibration direction of the diaphragm 21J of the above mentioned speaker device is determined by: the total of the length of the cone-shaped diaphragm 21J in the vibration direction and the height (a) of the edge 4J through which the diaphragm 21J is supported by the frame 3J; the distance (b) in the vibration direction from the junction of the diaphragm 21j and damper 7J to the plate 53J of the magnetic circuit; the winding width (c) of the voice coil 611J; the distance (d) in the vibration direction from the bottom of the voice coil 611J to the yoke 51J of the magnetic circuit; the thickness (e) of the yoke of the magnetic circuit; the maximum amplitude of the voice coil bobbin 610J while the speaker is driven; the thickness of the frame 3J supporting the diaphragm 21J and the magnetic circuit, and the like.
Particularly, in a loud speaker device, it is necessary to increase the distance (b) in the vibration direction from the junction of diaphragm 21J to damper 7J, the winding width (c) of the voice coil 611J, the distance (d) in the vibration direction from the bottom of the voice coil 611J to the yoke 51J of the magnetic circuit, and the like, and the dimension (sound emission direction) in the vibration direction of the diaphragm 21J is relatively large.
That is, since the above mentioned speaker device is configured such that the vibration direction of the voice coil bobbin 610J and the vibration direction of the diaphragm 21J become substantially parallel, it is relatively difficult to manage a thinner and larger sound-volume loudspeaker.
Also, in the typical dynamic speaker device, since the voice coil bobbin 610J is joined to an inner periphery of the cone-shaped diaphragm 21J and a driving force is transmitted from the voice coil bobbin 610J to the inner periphery of the diaphragm 21J, it is relatively difficult to drive the entire diaphragm substantially in-phase. Therefore, a speaker device allowing the entire diaphragm to be vibrated substantially in-phase is desirable.
As a flat speaker device, there is known an electrostatic speaker device. The electrostatic speaker device has such a structure that a diaphragm (movable electrode) and a fixed electrode are arranged opposite to each other. In this speaker device, the diaphragm is displaced by application of a DC voltage across the electrodes, and when a signal superimposed with an audio signal is input to the electrodes, the diaphragm vibrates in response to the signal.
In the above mentioned electrostatic speaker device, however, if an audio signal of relatively large amplitude is input, a driving force may nonlinearly vary considerably and thereby quality of a reproduced sound may be relatively deteriorated.